Conventional wheelchairs have two pairs of wheels, namely a rear pair of wheels with two large rear wheels, which can be manually driven, and a front pair of wheels, whose shafts can turn in a horizontal plane around a turning point. These wheelchairs are generally foldable and to this end have transverse supports made of two hingedly connected elements, each one of which is hinged on a longitudinal support. Therefore the width of this wheelchair is reduced when it is folded up. The disadvantage of these foldable wheelchairs lies in their lack of rigidity caused by the many hinged connections.
To remedy this disadvantage, it was attempted to produce wheelchairs with rigid and preferably closed frames. For example, a wheelchair of the type described at the outset was described in Swiss Patent Application 1547/97, whose frame is closed and therefore comparatively rigid. This frame consists of a front horizontal transverse support at the height of the feet of the user, a rear horizontal transverse support formed by an axle tube of the pair of rear wheels, and two L-shaped lateral supports, each one of which connects one end of the front transverse support with an end of the rear transverse support, and wherein each lateral support has an upright leg and a longitudinal leg. A front wheel arrangement with a single, centered front wheel, or two front wheels spaced apart from each other, is fastened on the front transverse support. This wheelchair has great rigidity and is easy to turn and maneuver, thanks to the front wheel arrangement which is generally placed in the central area of the front transverse support. It is mainly used as a sport wheel chair. The disadvantage of this wheelchair mainly lies in its poor tilting stability; it is therefore of less use for everyday use and is considered to be unusable by greatly handicapped and older users.